Darlington drivers who park and leave their engines running could be liable to an on-the-spot fine before the end of the year.

The move follows the introduction of the Road Traffic (Vehicle Emissions Fixed Penalty) Regulations 2002, which allows local authorities to fine offenders if they refuse to switch off their engines.

The scheme, which is to be adopted nationally, aims to reduce exhaust emissions to help improve air quality.

Last year, Darlington recorded 20 days when air pollution exceeded recommended levels. The maximum number of days allowed under new government legislation is 12.

The town's uniformed wardens and car park patrol officers are expected to be authorised to issue fixed penalty notices when a car has left its engine running for more than a couple of minutes while parked.

Exemptions to the rule include vehicles queuing at traffic lights, refrigerated vehicles or vehicles carrying elderly or disabled people.

On a cold day, taxis would be allowed to keep their engines running while waiting at the rank and motorists would be able to run their engines to help defrost a windscreen.

Keith Atkinson, the council's head of environment regulatory services, told Darlington Transport Forum members on Monday that a common sense approach would be adopted.

"To help us improve air quality, the council has got to have the public on board. Everybody has to be reasonable.

"Fixed penalties of £20 will only be given to those drivers who refuse to co-operate, but the emphasis of the scheme is to encourage drivers to switch off. The fine will be the last resort."

Taxi and bus operators are to be consulted before the scheme goes into operation while a publicity campaign will run in the weeks leading up to its start date.

The proposal will now go to cabinet for formal approval and if adopted, it is likely to be implemented within six months.